Dynamic regenerative heat exchanger

ABSTRACT

Described is an axial, piston-type, dynamic regenerative heat exchanger.

United States Patent [191 Sawyer DYNAMIC REGENERATIVE HEAT EXCI-IANGER 1 Inventor: Kenneth W. Sawyer, Palos Verdes Peninsula, Calif.

Assignee: The Garrett Corporation, Los

Angeles, Calif.

Filed: Apr. 22, 1971 Appl. No.: 136,430

US. Cl 165/1, 165/6, 165/7, 165/10, 60/3951 Int. Cl. F28d 19/04 Field of Search 165/6, 7, 10, 8; 60/3951 R References Cited UNITED STATES PATENTS 12/1956 Holm 165/6 as {We 141 142 145 144 1 mg; 101 g {/9 141 July 16, 1974 2,892,615 6/1959 Misener 165/9 3,177,661 4/1965. Hasbrouck et al. 165/8 X Rl7,l [/1929 Murray /6 FOREIGN PATENTS OR APPLICATIONS 760,803 11/1956 Great Britain 165/7 675,305 12/1963 Canada 165/8 220,867 8/1924 Great Britain 165/6 675,408 7/1952 Great Britain 165/7 Primary Examiner-Albert W. Davis, Jr. Attorney, Agent, or Firm-Albert J. Miller Described is an axial, piston-type, dynamic regenerative heat exchanger.

ABSTRACT 10 Claims, 10 Drawing Figures PATENTEDJULI s 1914 SHEET 1 UPS PATENTEI] JUL I 6 I974 sum am 5 I BACKGROUND OF THE INVENTION It is generally desirable in the operation of a gas turbine, particularly a gas turbine directed towards a vehicular application, to utilize and recover the heat energy in the turbine exhaust gases by transferring this heat energy to the incoming air for the combustion chamber. One method of accomplishing this result is to utilize a fixed boundary recuperator of either tubular or plate-fin construction as a direct transfer heat exchanger in which the compressor discharge air and the turbine exhaust gas exchange thermal energy directly through, and separated by, the heat transfer surface itself.

Alternately, a periodic flow regenerator, consisting of matrix heat transfer surfaces periodically passed through the hot and cold flow streams and back again, 7

has been utilized. Generally, this is accomplished by first passing each increment or segment of a high heat capacity, fluid pervious matrix material'through azone defined by suitable ducts which constrain hot exhaust gases to pass through that matrix increment temporarily residing in the zone, and then moving the increment 'to a second zone, spaced from the first, through which a relatively cool fluid, for example air, is similarly ducted so as to pass through the previously heated matrix increment and thereby extract therefrom the heat energy thus stored in the matrix. This process is made continuous by again returning the matrix'increment to the same or a different hot gas zone and the cycle is repeated. Conventional regenerating devices of a rotary type, such that the matrix is arranged around a periphery of a torous-shaped rotary element, are described in US. Pat. Nos. 3,177,928; 3,326,274 and 3,367,403.

For the proper operation of a rotary regenerator, it is necessary to isolate the zones through which the hot and cool gases are passed so that leakage or by-pass does not occur directly from one to the other within the heat exchange device itself. While various seals have been developed for use between the relatively moving matrix material and stationary housing, none have proven to be satisfactory over any extended period of high temperature operating time.

SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 14 are axial sectional views of the dynamic regenerator of the present invention illustrating the pistons in various axial positions.

FIG. 5 is an isometric view of a turbomachine including the dynamic regenerator of FIGS. 1-4.

FIG. 6 is a sectional view of the turbomachine of FIG.

5 having a section of the dynamic regenerator taken generally along lines 6-6 of FIG. 3.

FIG. 7 is a sectional view of the dynamic regenerator taken generally along lines 7--7 of FIG. 3.

FIG. 8 is anisometric view of an individual C-shaped matrix package.

FIG. 9 is an axial sectional view of an alternate dynamic regenerator having 8 matrix packages.

FIG. 10 is an axial sectional view of another alternate dynamic regenerator having 11 matrix packages.

DESCRIPTION OF THE PREFERRED I EMBODIMENTS As shown inFIGS. 1-4, the regenerator 10 basically comprises a pair or pairs of axial piston assemblies 40, 42 slidably within a pair or pairs of piston cylinders 44, 46 in a regenerator housing 48. The housing 48 includes a central cold fluid manifold 50 to receive the flow of air to be heated, such as the compressed air from a compressor, and two hot fluid manifolds 52, 54,

one on either side of the central cold fluid manifold 50,

to receive the flow of hot fluid such as the exhaust gases from a turbine. Bulkheads 56, 58-are provided on either side of the cold fluid manifold 50 to provide flow separation from the hot fluid manifolds 52, 54. As shown by the arrows, the countercurrent flow directions of the cold and hot fluids are schematically illustrated.

- Piston assemblies 40, 42 are disposed in piston cylinders-44, 46 respectively for alternate reciprocal axial movement therein. Each piston assembly comprises a plurality of heat transfer matrix packages disposed between two piston end retainer members with adjacent matrix packages separated by piston rings. In the particular regenerator illustrated in FIGS. 1-4, piston assembly v40 includes Smatrix packages 60, 61, 62, 63 and 64, separated by piston rings '65, 66, 67 and 68 respectively. The matrix packages 60,. 61, 62, 63 and 64 are retained between end retainers 80, 81. Piston assembly 42 likewise has 5 matrix packages 70, 71, 72, 73 and 74 separated by piston rings 75, 76, 77 and 78 respectively. End retainers 82, 83 are positioned at either end of the piston assembly 42 matrix packages 70, 71, 72, 73 and 74.

For the purpose of explaining the operation of the 5 matrix package regenerator, the piston cylinders 44 and 46 have been designated with 15 equal positions 101 through 115 respectively, each equal position substantially equal to the length of a single matrix package. The piston cylinder end includes 4 positions 101, 102, 103 and 104; that is its length is equivalent to 4 matrix packages. The hot fluid manifold 52 represents two positions 105 and 106 while hot fluid manifold 54 likewise represents two positions and 111. Positions 107 and 109 represent bulkheads 56 and 58 respectively, while position 108 represents cold fluid manifold 50. The other piston cylinder end 91includes 4 positions 112, 113, 114 and 115. The piston assembly end retainers 80, 81, 82 and 83, while they cannot be assigned positions since they reciprocate back and forth in the piston cylinders, have a length equivalent to the combined length of 3 matrix packages or one matrix package length less than the piston cylinder ends 90, 91.

The axial movement of the piston assembly 40 and 42 is of an alternate reciprocal nature, that is, when piston assembly 40 is moving in one axial direction, piston assembly 42 is moving in the opposite axial direction. Using FIG. 1 as a starting or reference point, piston assembly 40 is at its extreme left-hand position while piston assembly 42 is in its extreme right-hand position. At this reference point, piston end retainer 80 occupies positions 101, 102 and 103; matrix package 60 occupies position 104; matrix packages 61 and 62 occupy positions 105 and 106 in the hot fluid manifold 52, matrix package 63 occupies position 107, matrix package 64 occupies position 108 in the cold fluid manifold 50 and end retainer 81 occupies positions 109, 110 and 111. Positions 112, 113, 114 and 115 are vacant. For piston assembly 42 at its extreme right-hand position, positions 101, 102, 103 and 104 are vacant, end retainer 82 occupies positions 105, 106 and 107; matrix package 70 occupies position 108 in the cold fluid manifold 50, matrix package 71 occupies position 109; matrix packages 72 and 73 occupy positions 110 and 111 in the hot fluid manifold 54; matrix package 74 oocupies position 112; and end retainer 83 occupies positions 113, 114 and 115.

In the initial reference piston assembly starting point of FIG. 1, matrix packages 61 and 62 of piston assembly 40 and matrix packages 72 and 73 of piston assembly 42 are being heated by the hot fluid in manifolds 52 and 54 respectively. At the same time, matrix package 64 of piston assembly 40 and matrix package 70 of piston assembly 42 are giving up heat to the cold fluid in manifold 50. In this initial piston assembly 40 position, piston rings 65 and 67 prevent leakage or carry over from the hot fluid from the fluid manifold 52 while piston ring 68 and retainer 81 prevent leakage or carry over of the cold fluid from the cold fluid manifold 50. The end retainer 81 effectively prevents hot fluid from hot fluid manifold 54 from entering piston cylinder 44.

With respect to piston assembly 42, end retainer 82 prevents hot fluid from hot fluid manifold 52 from entering piston cylinder 46 while piston rings 76 and 78 prevent leakage from the hot fluid manifold 54. Piston ring 75 and end retainer 82 prevent leakage or carry over from the cold fluid manifold 50.

In FIG. 2, piston assembly 40 has moved one position or matrix package length to the right while piston assembly 42 has moved one position to the left. In these positions, matrix packages 60 and 61 and 73 and 74 are heated by the hot fluid while matrix packages 63 and 71 are releasing heat to the cold fluid.

In FIG. 3, piston assembly 40 has moved a total of 2% positions to the right while piston assembly 42 has moved a total of 2% positions to the left from their respective initial reference positions. The purpose of illustrating the piston assemblies 40 and 42 in a half position is to demonstrate the sealing of the piston rings during the travel between positions. It can be seen that piston rings 65 and 76 prevent leakage between hot fluid manifold 52 and cold fluid manifold 50 while piston rings 67 and 78 prevent leakage between hot fluid 'manifold 54 and cold fluid manifold 50.

FIG. 4 illustrates piston assembly 40 at its extreme right-hand position and piston assembly 42 at its extreme left-hand position, both a total of 4 positions removed from their initial reference positions. Upon as they pass through position 108 in the cold fluid manifold 50. In the return trip to the left, matrix packages 62, 63 and 64 will pick up heat in positions 110 and 111 and give up this heat to the cold fluid as they move to the left through position 108 in the cold fluid manifold 50. The back and forth movement of piston assembly 42,.exactly out of phase with the movement of piston assembly 40, will subject matrix packages 70, 71, 72, 73 and 74 alternately to hot and cold fluid in the same manner.

At all times during the alternate reciprocal movement of piston assemblies 40 and 42, two matrix package lengthsof matrix material from piston assembly 40 and a like amount of matrix material from piston assembly 42 will be subjected to hot fluid from hot fluid manifolds 52 and 54. Thus a total of 4 matrix package lengths of matrix material are always being heated by the hot fluid. At the same time one matrix package length of matrix material from each piston assembly is always being subjected to cold fluid fromthe cold fluid manifold 50. Therefore, a total of two matrix package lengths of matrix material are releasing heat to the cold fluid.

The dynamic regenerative heat exchanger can be used in a great number of heat exchanger applications including as an intercooler, an industrial-or domestic air preheater, a process air to air unit or as a gas turbine regenerator. The following detailed description of the dynamic regenerative heat exchanger is directed to a gas turbine regeneratoralthough itis equally applicable to all of the other applications.

As illustrated in FIG. 5, the dynamic regenerative heat exchanger or regenerator 10 can be mounted at the discharge-end 11 of turbomachine 12. A piston actuating mechanism 14 is mounted at one end of the dynamic regenerator 10 to provide alternate reciprocating linear motion to the pistons within the regenerator. The piston actuating mechanism 14 may be a direct gear drive from an auxiliary turbomachine shaft or alternately, hydraulic, pneumatic, or electrical motors may be provided.

As shown in more detail in FIG. 6, the turbomachine 12 may comprise a compressor 16 having an air inlet 20 to a single radial stage 18. A regenerator duct 22 transfers the compressed air from the compressor discharge collector 24 tothe compressed air inlet 26 then to the cold fluid manifold 50 of the regenerator 10. The compressor discharge air flows radially outward through the matrices 61, 72 of the pistons 40, 42 respectively of the dynamic regenerator 10. The heated compressed air from the regenerator 10 is then passed to the gas generator inlet scroll 30. Following combustion in the combustor 31, the combustion gases pass through the blades 32 of the turbine 34.

Following combustion and passage through the turbine 34, the exhaust gases are directed through the hot fluid manifolds 52 and 54 of the regenerator which are mounted at the discharge end 11 of the turbomachine 12. As shown in FIG. 7, the hot exhaust gases pass radially inward through heat transfer matrices 63, 74 of pistons 40, 42 respectively before passing from the regenerator through exit ducts 36, 38.

The individual matrix packages may be straight axial matrices of a C" configuration as shown in FIGS. 6 and 7 or may be axially convoluted to increase the flow frontal area andthus reduce piston length. While these figures show the cold fluid flowing radially outward and the hot fluid flowing radially inward, this relationship can be reversed to meet specific applications. Pearshaped flow splitting lobes 59 may be provided to more evenly distribute the flow through the matrices. Secondary seals 55, 57 of a labyrinth type may be utilized at 5 ing:

the open end of the C-shaped matrices.

Practically any type of matrix material can be packaged within the C-shaped piston since the matrix is not a structural element. The matrix material can be selected solely on the basis of its heat transfer performance, weight, and volume. It is not called upon to prevent leakage, support seals, or carry mechanical and transmission loads. Matrix cores consisting of triangular fins, wavy or offset fins, woven wire screens, crossed rods, packed spheres, or glass-ceramic cellular structures can be utilized. Wire wrapped screen matrices can be wrapped tightly to form a large matrix face area in a small diameter at low cost with small carry over losses. An isometric view of a C-shaped wire wrapped screen is shown in FIG. 8.

Inherent in the dynamic regenerator is a true counterflow heat exchange condition, that is two fluid streams moving in direct opposition to each other. Heat is absorbed on the surfaces of the matrices moving through the hot exhaust gases and subsequently released to the compressor discharge air as a result of the continued axial movement of the matrices. Synchronization of the axial piston movement motivates the matrices alternately between hot and cold fluid streams and provides a self-cleaning action which insures that no fouling or clogging will occur in any of the matrices.

' type of regenerator which requires face seals. The axial piston ring art is highly developed for automotive and aircraft reciprocating engines which have velocities in the order of 30 ft./sec. Unlike the rotary regenerator,

, no rubbing seal is necessary between the matrix surface itself and the housing. There should be no thermal distortion of the seal rubbing surfaces. I

While a 5 matrix package regenerator as shown in FIGS. 1-4 has been described in considerable detail and its operation provided, the number of matrix packages can be varied considerably. For example, an 8 matrix package regenerator as shown in FIG. 9 and an 11 matrix package regenerator as shown in FIG. 10 can be employed. It is possible to construct regenerators having virtually any number of matrix packages, e.g., 3, 5, 8, 9, 11, etc. There are practical limitations that make a 5, 8 or 11 matrix package most attractive. The greater the number of packages, the shorter the overall length of the regenerator and the smaller the carry over losses between the-hot and cold fluids.

The dynamic regenerator provides a continuous flow device (no pulsing) that can be easily packaged for efficient heat exchange and can be easily integrated with associated turbomachinery. It has numerous advantages over equivalent rotary type regenerators and fixed boundary recuperators.

While specific embodiments of the invention have been illustrated and described, it is to be understood that these embodiments are provided by way of example only and that the invention is not to be construed 6 as being limited thereto, but only by the proper scope of the following claims. 1

What I claim is:

l. A dynamic regenerative heat exchanger comprisa housing defining a pair of piston cylinders, said housing having a central cold fluid manifold and two hot fluid manifolds, one hot fluid manifold disposed on either side of said cold fluid manifold, each of said manifolds extending across both of said pair of piston cylinders; and

a pair of piston assemblies disposed within said pair of piston cylinders to alternately reciprocate therein, said piston assemblies each including at least five substantially C-shapedheat transfer matrices of 'a fluid permeable material to alternately reciprocate between one of said hot fluid manifolds and said cold fluid manifold, cold fluid from said cold fluid manifold physically passing through the fluid permeable C-shaped matrices material in one direction and hot fluid from said hot fluid manifolds physically passing through the fluid permeable C-shaped matrices material in the other direction;

2. The dynamic regenerative heat exchanger of claim 1 wherein cold fluid from said cold fluid manifold flows radially outward successively through said matrices material of both of said pair of piston assemblies during reciprocation thereof and the hot fluid from said hot fluid manifold flows radially inward successively through said matrices material of both of said pair of piston assemblies during reciprocation thereof.

3. The dynamic regenerative heat exchanger of claim 1 wherein cold fluid from said cold fluid manifold flows radially inward successively through said matrices material of both of said pair of piston assemblies during reciprocation thereof 'and the hot fluid from said hot fluid manifold flows radially outward successively through said matrices material of both of said pair of piston assemblies during reciprocation thereof.

4. The dynamic regenerative heat exchanger of claim land in addition, means operably associated with said housing and said pair of piston assemblies to alternately reciprocate said pair ofpiston assemblies with said pair of piston cylinders.

5. A dynamic regenerative heat exchanger comprisa housing defining a pair of piston cylinders, said housing having a central cold fluid manifold and two hot fluid manifolds, one hot fluid manifold disposed on either side of said cold fluid manifold, each of said manifolds extending across both of said pair of piston cylinders; and

a pair of piston assemblies disposed within said pair of piston assemblies to alternately reciprocate therein, each assembly having at least five substantially C-shaped heat transfer matrices of a fluid permeable material disposed between two end retainers with adjacent matrices separated by a piston ring to prevent the flow of fluid between adjacent matrices, each heat transfer matrix to alternately reciprocate between one of said hot fluid manifolds and said cold fluid manifold.

6. The combination of claim 5 wherein said C-shaped heat transfer matrices include flow splitting lobes.

7. Av dynamic regenerative heat exchanger compris- 3,823 ,766 t 7 8 a pair of piston assemblies, each assembly having at least five substantially equal length, generally C- shaped heat transfer matrices disposed between two end I retainers, each end retainer having a length substantially equal to at least three heat transfer matric lengths, each of said pair of piston assemblies including at least four piston rings, one piston ring disposed between adjacent heat transfer matrices; and a housing defining a pair of piston cylinders in which 10 through the heattransfer matrices previously heated in the exhaust gas manifolds whereby the air recovers thermal energy from said heat transfer matrices, one exhaust gas manifold disposed on either side of said central air manifold.

9. A dynamic regenerative heat exchanger comprisa housing defining a first piston cylinder having a longitudinal axis and a second substantially identical to receive the air for combustion and pass the air said-pair of piston assemblies are disposed to oppositely reciprocate,

said housing having a central cold fluid manifold having an opening to direct the flow of cold fluid in piston cylinder having a longitudinal axis substantially parallel to the longitudinal axis of said first piston cylinder;

said housing having a central cold fluid manifold to one direction across said pair of piston cylinders direct the flow of a cold fluid transverse), across slibstannany equal to a} least 9 heat transffr the longitudinal'axes of said first and said second mx f hot fluld mamfolds g having an piston cylinders in one direction and having two Opening. to (.hrect the w hot i hot fluid manifolds to direct the flow of a hot fluid posed ectlon across Sald pan of plston cylmders transversely across the longitudinal axes of said slibstamlany equal to at.least V a transfer fl' second and said first piston cylinders in a direction mx lellgths hot mamfolq dlspqsed on opposite to the flow of the cold fluid, one hot fluid ther slde of Sald cqmml cold fluld marilfold two manifold disposed on either side of said cold fluid bulkheads each havmg a length substantially equal manifold, and

to at least one heat transfer matrix length disposed on either side of said central cold fluid manifold befirst and a second plston assembly each havmg at tween said central coldfluid manifold and said hot fluid manifolds, and two end portions disposed at either end of said pair of piston cylinders, each end least five substantially C-shaped heat transfer matrices of a fluid permeable material, said first piston assembly disposed within said first piston cylinder to reciprocate therein along the longitudinal axis portion having a length substantially equal to at least four heat transfer matric lengths; during the opposed reciprocation of said pair of piston assemblies at least two heat transfer matrices of each pistonassembly exposed to the flow of hot fluid and at least one heat transfer matrix of each piston assembly exposed to the flow of cold fluid.

thereof, and said second piston assembly disposed within said second piston cylinder to reciprocate therein along the longitudinal axis thereof oppositely to said first piston assembly, the matrices of said first and said second piston assemblies alternating between said cold fluid manifold and said hot fluid manifold.

10. A method of transferring thermal energy between a hot fluid and a cold fluid comprising:

defining a pair of substantially identical piston cylinders having substantially parallel longitudinal axes in a housing;

providing acentral cold fluid manifold in said housing to direct a flow of cold fluid transversely across both of the pair of piston cylinders in one direction;

8. In combination:

a gas turbine, including a fuel-air combustor, to produce. shaft power and hot exhaust gases;

a compressor operably associated with said gas tur- 40 bine to supply compressed air to the fuel-air combustor of said gas turbine; and

a dynamic regenerative heat exchanger comprising,

a pair of piston assemblies each having at least five substantially C-shaped heat transfer matrices of a fluid permeable material therein andincluding flow splitting lobes, and a housing defining a pair of piston cylinders in which said pair of piston assemblies are disposed to alternately reciprocate, said housing having two exhaust gas manifolds to receive the exhaust gases from said turbomachine and pass the exhaust gases through the heat transfer matrices of said pair of piston assemblies alternately reciprocating through said exhaust gas manifolds whereby said heat transfer matrices recover thermal energy cold fluid manifold and said hot fluid manifolds. from said exhaust gases, and a central air manifold providing two hot fluid manifolds in said housing, one on either side of said central cold fluid manifold, to direct the flow of hot fluid transversely across both of the pair of piston cylinders in a direction opposed to the flow of cold fluid therethrough; and

oppositely reciprocating a pair of piston assemblies, each having at least five substantially C-shaped heat transfer matrices of a fluid permeable material, in said pair of piston cylinders between said 

1. A dynamic regenerative heat exchanger comprising: a housing defining a pair of piston cylinders, said housing having a central cold fluid manifold and two hot fluid manifolds, one hot fluid manifold disposed on either side of said cold fluid manifold, each of said manifolds extending across both of said pair of piston cylinders; and a pair of piston assemblies disposed within said pair of piston cylinders to alternately reciprocate therein, said piston assemblies each including at least five substantially C-shaped heat transfer matrices of a fluid permeable material to alternately reciprocate between one of said hot fluid manifolds and said cold fluid manifold, cold fluid from said cold fluid manifold physically passing through the fluid permeable Cshaped matrices material in one direction and hot fluid from said hot fluid manifolds physically passing through the fluid permeable C-shaped matrices material in the other direction.
 2. The dynamic regenerative heat exchanger of claim 1 wherein cold fluid from said cold fluid manifold flows radially outward successively through said matrices material of both of said pair of piston assemblies during reciprocation thereof and the hot fluid from said hot fluid manifold flows radially inward successively through said matrices material of both of said pair of piston assemblies during reciprocation thereof.
 3. The dynamic regenerative heat exchanger of claim 1 wherein cold fluid from said cold fluid manifold flows radially inward successively through said matrices material of both of said pair of piston assemblies during reciprocation thereof and the hot fluid from said hot fluid manifold flows radially outward successively through said matrices material of both of said pair of piston assemblies during reciprocation thereof.
 4. The dynamic regenerative heat exchanger of claim 1 and in addition, means operably associated with said housing and said pair of piston assemblies to alternately reciprocate said pair of piston assemblies with said pair of piston cylinders.
 5. A dynamic regenerative hEat exchanger comprising: a housing defining a pair of piston cylinders, said housing having a central cold fluid manifold and two hot fluid manifolds, one hot fluid manifold disposed on either side of said cold fluid manifold, each of said manifolds extending across both of said pair of piston cylinders; and a pair of piston assemblies disposed within said pair of piston assemblies to alternately reciprocate therein, each assembly having at least five substantially C-shaped heat transfer matrices of a fluid permeable material disposed between two end retainers with adjacent matrices separated by a piston ring to prevent the flow of fluid between adjacent matrices, each heat transfer matrix to alternately reciprocate between one of said hot fluid manifolds and said cold fluid manifold.
 6. The combination of claim 5 wherein said C-shaped heat transfer matrices include flow splitting lobes.
 7. A dynamic regenerative heat exchanger comprising: a pair of piston assemblies, each assembly having at least five substantially equal length, generally C-shaped heat transfer matrices disposed between two end retainers, each end retainer having a length substantially equal to at least three heat transfer matric lengths, each of said pair of piston assemblies including at least four piston rings, one piston ring disposed between adjacent heat transfer matrices; and a housing defining a pair of piston cylinders in which said pair of piston assemblies are disposed to oppositely reciprocate, said housing having a central cold fluid manifold having an opening to direct the flow of cold fluid in one direction across said pair of piston cylinders substantially equal to at least one heat transfer matrix length, two hot fluid manifolds each having an opening to direct the flow of hot fluid in an opposed direction across said pair of piston cylinders substantially equal to at least two heat transfer matrix lengths, one hot fluid manifold disposed on either side of said central cold fluid manifold, two bulkheads each having a length substantially equal to at least one heat transfer matrix length disposed on either side of said central cold fluid manifold between said central cold fluid manifold and said hot fluid manifolds, and two end portions disposed at either end of said pair of piston cylinders, each end portion having a length substantially equal to at least four heat transfer matric lengths; during the opposed reciprocation of said pair of piston assemblies at least two heat transfer matrices of each piston assembly exposed to the flow of hot fluid and at least one heat transfer matrix of each piston assembly exposed to the flow of cold fluid.
 8. In combination: a gas turbine, including a fuel-air combustor, to produce shaft power and hot exhaust gases; a compressor operably associated with said gas turbine to supply compressed air to the fuel-air combustor of said gas turbine; and a dynamic regenerative heat exchanger comprising, a pair of piston assemblies each having at least five substantially C-shaped heat transfer matrices of a fluid permeable material therein and including flow splitting lobes, and a housing defining a pair of piston cylinders in which said pair of piston assemblies are disposed to alternately reciprocate, said housing having two exhaust gas manifolds to receive the exhaust gases from said turbomachine and pass the exhaust gases through the heat transfer matrices of said pair of piston assemblies alternately reciprocating through said exhaust gas manifolds whereby said heat transfer matrices recover thermal energy from said exhaust gases, and a central air manifold to receive the air for combustion and pass the air through the heat transfer matrices previously heated in the exhaust gas manifolds whereby the air recovers thermal energy from said heat transfer matrices, one exhaust gas manifold disposed on either side of said central air manifold.
 9. A dynamic regenerative heat exchanger compRising: a housing defining a first piston cylinder having a longitudinal axis and a second substantially identical piston cylinder having a longitudinal axis substantially parallel to the longitudinal axis of said first piston cylinder; said housing having a central cold fluid manifold to direct the flow of a cold fluid transversely across the longitudinal axes of said first and said second piston cylinders in one direction and having two hot fluid manifolds to direct the flow of a hot fluid transversely across the longitudinal axes of said second and said first piston cylinders in a direction opposite to the flow of the cold fluid, one hot fluid manifold disposed on either side of said cold fluid manifold; and a first and a second piston assembly each having at least five substantially C-shaped heat transfer matrices of a fluid permeable material, said first piston assembly disposed within said first piston cylinder to reciprocate therein along the longitudinal axis thereof, and said second piston assembly disposed within said second piston cylinder to reciprocate therein along the longitudinal axis thereof oppositely to said first piston assembly, the matrices of said first and said second piston assemblies alternating between said cold fluid manifold and said hot fluid manifold.
 10. A method of transferring thermal energy between a hot fluid and a cold fluid comprising: defining a pair of substantially identical piston cylinders having substantially parallel longitudinal axes in a housing; providing a central cold fluid manifold in said housing to direct a flow of cold fluid transversely across both of the pair of piston cylinders in one direction; providing two hot fluid manifolds in said housing, one on either side of said central cold fluid manifold, to direct the flow of hot fluid transversely across both of the pair of piston cylinders in a direction opposed to the flow of cold fluid therethrough; and oppositely reciprocating a pair of piston assemblies, each having at least five substantially C-shaped heat transfer matrices of a fluid permeable material, in said pair of piston cylinders between said cold fluid manifold and said hot fluid manifolds. 